Immune-related diseases (e.g., cancer) are the manifestation or consequence of complex biological pathways, which in normal physiology are critical for responding to insult or injury, initiating repair from insult or injury, and mounting innate and acquired defenses. Disease or pathology occurs when these normal physiological pathways cause additional insult or injury that is directly related to the intensity of the response (e.g., as a consequence of abnormal regulation or excessive stimulation) or as a reaction to self.
Although the genesis of these diseases often involves multi-step pathways and often multiple different biological systems/pathways, intervention at critical points in one or more of these pathways can have an ameliorative or therapeutic effect. Therapeutic intervention can occur by either antagonism of a detrimental process/pathway or stimulation of a beneficial process/pathway.
Many immune-related diseases are known and have been extensively studied. Such diseases include cancer (neoplasia), immune-mediated inflammatory diseases, non-immune-mediated inflammatory diseases, infectious diseases, and immunodeficiency diseases.
T lymphocytes (T cells) are an important component of a mammalian immune response. T cells recognize antigens that are associated with a self-molecule encoded by genes within the major histocompatibility complex (MHC). The antigen may be displayed together with MHC molecules on the surface of antigen presenting cells (APCs), virus infected cells, cancer cells, grafts, etc. The T cell system eliminates these altered cells, which pose a health threat to the host mammal. T cells include helper T cells and cytotoxic T cells. Helper T cells proliferate extensively following recognition of an antigen-MHC complex on an APC. Helper T cells also secrete a variety of cytokines (i.e., lymphokines), which play a central role in the activation of B cells, cytotoxic T cells, and a variety of other cells that participate in the immune response.
Regulatory T cells (Treg) are a subset of helper T cells that play a critical role in inhibition of self-reactive immune responses and are often found in sites of chronic inflammation such as in tumor tissue. Tregs are defined phenotypically by high cell surface expression of CD25, CLTA4, GITR, and neuropilin-1 (NRP-1), and are under the control of the transcription factor FOXP3. Tregs perform their suppressive function on activated T cells through contact-dependent mechanisms and cytokine production. Tregs also modulate immune responses by direct interaction with ligands on dendritic cells (DCs), such as CD40L ligation and CTLA4 interaction with B7 molecules on DCs that elicits the induction of indoleamine 2,3-dioxygenase (IDO). DCs are professional APCs capable of inducing immunity or tolerance against self or non-self antigens. DC-expanded Tregs suppress alloreactivity responses in vitro, and when adoptively transferred, appropriate Tregs inhibited diabetes in NODscid mice or experimentally induced asthma. Specific interactions of ligands on DC with Tregs can also abrogate their suppressive function, such as engagement of GITR in mice, suggesting DC may have a pluralistic role in modulating Treg function.
The molecules CTLA4 and GITR are representative of ligands defined within the CD28-B7 and TNF-superfamilies of co-stimulatory/-inhibitory molecules, respectively. These molecules are highly expressed on Tregs but are typically upregulated on activated T cells. More recently, a protein designated TIGIT (for T-cell immunoreceptor with Ig and ITIM domains) was identified as a cell surface-bound protein specifically expressed in T cells that possessing an IgV domain, a transmembrane domain, and two putative immunoreceptor tyrosine inhibitory (ITIM) motifs. TIGIT was shown to be particularly expressed on Treg and memory T cell subsets, as well as NK cells. As there is an unmet need for new therapeutics and methods of treatment of immune-related disorders and particularly cancers, described herein are unexpectedly efficacious therapeutic compositions, such as the anti-TIGIT antibodies and compositions thereof, and methods of treatment of immune-related disorders and cancers, which involve modulating the interaction of TIGIT with its binding partners.